Modelling Of Concurrent Systems

The cooperation test [Apt, Francez & de Roever] was originally conceived to capture the proof theoretical analogue of distributed message exchange between disjoint processes, as opposed to the interference freedom test [Owicki & Gries], being the proof theoretical analogue of concurrent communication by means of interference through jointly shared variables. Some authors ([Levin & Gries, Lamport & Schneider, Schlichting and Schneider]) stress that both forms of communication can be proof theoretically characterized using interference freedom only, since proofs for both ultimately amount to an invariance proof of a big global assertion [Ashcroft], invariance of whose parts amounts to interference freedom. Yet I feel that the characteristic nature of the cooperation test is still preserved in the analysis of these authors, because in their analysis of CSP the part dealing with interference freedom specializes to maintenance of a global invariant, the expression of which requires per process the introduction of auxiliary variables which are updated in that process only, thus preserving the concept of disjointness (as opposed to sharing), since now all variables from different processes are disjoint. The cooperation test has been applied to characterize concurrent communication as occurring in Hoare's Communicating Sequential Processes (CSP) [Hoare 2], Ichbiah's ADA [ARM], and Brinch Hansen's Distributed Processes (DP) [Brinch Hansen]. This characterization has been certified through soundness and completeness proofs [Apt 2, Gerth]. As in the interference freedom test this characterization consists of two stages, a local sequential stage and a global stage.

This book uses a variety of applications to illustrate a modeling method that helps practitioners to manage complex software-intensive systems. The proposed method relies on the combination of its abstraction concept and its operational character, with behavioral models in the precise and simple form of Abstract State Machines (ASMs). The book introduces both the modeling method (Part I) and the available tool support (Part II): In Part I the authors detail (using numerous examples) how to construct, explain, debug, explore, extend and reuse accurate system design models, starting from scratch. Only an elementary knowledge of common mathematical (including set-theoretic) notation and some basic experience with computational processes (systems, programs, algorithms) is assumed. Part II then shows how the modeling method can be supported by implementing tools that make design models executable and debuggable. To illustrate how to build, debug and maintain systems and to explain their construction in a checkable manner, a general, problem-oriented refinement method is adopted to construct system models from components. The method starts with abstract models and refines them step by step, incrementally adding further details that eventually lead to code. Intended for practitioners who build software intensive systems, and students specializing in software engineering, it can be used both for self-study and for teaching, and it can serve as a reference book. Exercises are included to help readers check their understanding of the explained concepts. For many models defined in the book, refinements to executable versions can be downloaded for experimental validation from the book’s website at http://modelingbook.informatik.uni-ulm.de

Intheworldweliveinconcurrencyisthenorm.Forexample,thehumanbody isamassivelyconcurrentsystem,comprisingahugenumberofcells,allsim- taneously evolving and independently engaging in their individual biological processing.Inaddition,inthebiologicalworld,trulysequentialsystemsrarely arise. However, they are more common when manmade artefacts are cons- ered. In particular, computer systems are often developed from a sequential perspective. Why is this? The simple reason is that it is easier for us to think about sequential, rather than concurrent, systems. Thus, we use sequentiality as a device to simplify the design process. However, the need for increasingly powerful, ?exible and usable computer systems mitigates against simplifying sequentiality assumptions. A good - ample of this is the all-powerful position held by the Internet, which is highly concurrent at many di?erent levels of decomposition. Thus, the modern c- puter scientist (and indeed the modern scientist in general) is forced to think aboutconcurrentsystemsandthesubtleandintricatebehaviourthatemerges from the interaction of simultaneously evolving components. Over a period of 25 years, or so, the ?eld of concurrency theory has been involved in the development of a set of mathematical techniques that can help system developers to think about and build concurrent systems. These theories are the subject matter of this book.

CSP notation has been used extensively for teaching and applying concurrency theory, ever since the publication of the text Communicating Sequential Processes by C.A.R. Hoare in 1985. Both a programming language and a specification language, the theory of CSP helps users to understand concurrent systems, and to decide whether a program meets its specification. As a member of the family of process algebras, the concepts of communication and interaction are presented in an algebraic style. An invaluable reference on the state of the art in CSP, Understanding Concurrent Systems also serves as a comprehensive introduction to the field, in addition to providing material for a number of more advanced courses. A first point of reference for anyone wanting to use CSP or learn about its theory, the book also introduces other views of concurrency, using CSP to model and explain these. The text is fully integrated with CSP-based tools such as FDR, and describes how to create new tools based on FDR. Most of the book relies on no theoretical background other than a basic knowledge of sets and sequences. Sophisticated mathematical arguments are avoided whenever possible. Topics and features: presents a comprehensive introduction to CSP; discusses the latest advances in CSP, covering topics of operational semantics, denotational models, finite observation models and infinite-behaviour models, and algebraic semantics; explores the practical application of CSP, including timed modelling, discrete modelling, parameterised verifications and the state explosion problem, and advanced topics in the use of FDR; examines the ability of CSP to describe and enable reasoning about parallel systems modelled in other paradigms; covers a broad variety of concurrent systems, including combinatorial, timed, priority-based, mobile, shared variable, statecharts, buffered and asynchronous systems; contains exercises and case studies to support the text; supplies further tools and information at the associated website: http://www.comlab.ox.ac.uk/ucs/. From undergraduate students of computer science in need of an introduction to the area, to researchers and practitioners desiring a more in-depth understanding of theory and practice of concurrent systems, this broad-ranging text/reference is essential reading for anyone interested in Hoare’s CSP.

Concurrent systems are generally understood in terms of behavioral notions. Models for Concurrency analyzes the subject in terms of events and their temporal relationship rather than on global states. It presents a comprehensive analysis of model theory applied to concurrent protocols, and seeks to provide a theory of concurrency that is both intuitively appealing and rigorously based on mathematical foundations. The book is divided into three main sections. The first introduces the required concepts from model theory, details the structures that are used to model concurrency, gives an in-depth description and explanation of the semantics of a simple language that allows concurrent execution of sequential programs, and deals with the question of resolving executions into higher-level and lower-level granularities. The second and third sections apply the theory developed to practical examples, and an exposition of the producer/consumer problem with details of two solutions is given. The author also deals with message passing, as opposed to shared memory.

This volume presents carefully refereed versions of the best papers presented at the Workshop on Models and Languages for Coordination of Parallelism and Distribution, held during ECOOP '94 in Bologna, Italy in July 1994. Recently a new class of models and languages for distributed and parallel programming has evolved; all these models share a few basic concepts: simple features for data description and a small number of mechanisms for coordinating the work of agents in a distributed setting. This volume demonstrates that integrating such features with those known from concurrent object-oriented programming is very promising with regard to language support for distribution and software composition.